Our principal objective is to examine the electron microscopical structure of Sertoli cells and germ cells, in rodents and primates, and to correlate the structure of these seminiferous elements with the varied functions. Eight functions have been attributed to the Sertoli cells; using control and experimental models we will attempt to relate morphological features of the nucleus and cytoplasm with each of the functions. We propose to study the development of the Sertoli cell from birth to adulthood and to determine whether exogenously added follicle stimulating hormone (FSH) directly affects its fine structure. Biochemical data revealed that the Sertoli cell is the principal target for FSH in the testis. A main effort of this proposal will be to localize testosterone to specific cell types in the seminiferous epithelium, using electron microscopic methods. In a preliminary examination of the fine structure of monkey germ cells we noted a marked absence of cellular organelles in spermatogonia and a very imp essive array of smooth endoplasmic reticulum (SER) in spermatids. The SER weas very closely associated with the developing acrosomic system and with the motile sperm flagellum. It is tempting to speculate that this cytoplasmic organelle may be involved in the elaboration of these two important components of the spermatozoon. Furthermore, the enzymes necessary for steroid metabolism have been localized to smooth endoplasmic reticulum. We would like to initiate a comparative analysis of the fine structure of the organelles present in spermatogonia, spermatocytes and spermatids in the primate. Most investigators believe that steroid metabolism within the seminiferous epithelium is principally carried out by the Sertoli cells. It will be interesting to isolate the smooth endoplasmic reticulum of spermatids and attempt to determine whether it possesses the steroid metabolizing enzymes as well.